In a recent paper, Khilyuk and Chilingar (2006) promote their view that the human influence on climate is negligible compared to natural forces driving the Earth’s climate. They conclude from this opinion that measures to reduce carbon dioxide emissions, such as defined by the Kyoto Protocol, are merely a waste of money. The scope of the paper is very broad, covering topics such as the Earth’s radiation balance, the influence of changing orbital parameters on insolation, the entire history of the Earth’s degassing and the composition of the atmosphere, the internal heat sources of the Earth, the role of the ocean and microbial activities in the climate system, and the temperature history of the last millennia. The hypotheses put forward by Khilyuk and Chilingar (2006) on these topics are not only unusual, but unfortunately in many points misleading, inconsistent, or even plainly wrong, as will be shown in the following. At the very least, the authors fail to adequately represent the...